The present invention relates to an engine control apparatus of a vehicle having an air conditioner, and more particularly, to an engine control apparatus in a vehicle that has an air conditioner having a variable displacement compressor that is driven by a vehicle engine.
A vehicle air conditioner that predicts the actual torque of a compressor when the compressor is started based on a predetermined torque has been proposed. In the vehicle using the air conditioner, the engine is controlled to produce extra torque for driving the compressor.
If a variable displacement compressor is used, it is difficult to control the engine to produce an extra torque that is accurately corresponds to the torque required for driving the compressor.
The displacement of a variable displacement compressor corresponds to the torque of the compressor. The torque required to drive the compressor greatly varies between when the displacement is minimum and when the displacement is maximum. Therefore, if the compressor driving torque is predicted based on a predetermined fixed value, the predicted torque may be significantly different from the actual torque. As a result, starting the air conditioner while the vehicle is running may change the vehicle speed. Also, starting the air conditioner while the vehicle is accelerating may hinder the responsiveness of the vehicle.
Accordingly, in a vehicle that has an air conditioner having a variable displacement compressor driven by an engine, it is an objective of the present invention to provide an engine control apparatus that accurately predicts the driving torque of the variable displacement compressor.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an engine control apparatus of a vehicle having an air conditioner is provided. The air conditioner includes a variable displacement compressor, a pressure difference detection device, a control valve, a sensor and a temperature adjuster. The compressor is driven by the engine and includes a crank chamber and a cam plate accommodated in the crank chamber. The displacement of the compressor is varied by changing the pressure in the crank chamber. The compressor, together with the external refrigerant circuit, forms a refrigeration circuit. The pressure difference detection device detects the difference between the pressures at two pressure monitoring points, which are located in the refrigeration circuit. The pressure difference represents the displacement of the compressor. The control valve has a valve portion and a solenoid. The valve portion automatically adjusts its opening size based on the pressure difference detected by the pressure difference detection device. The solenoid changes a target pressure difference, which is used as a reference value for adjusting the opening size of the valve portion. The sensor outputs a signal that represents the temperature of the passenger compartment. The engine control apparatus includes a controller. The controller compares the signal from the sensor with a signal from the temperature adjuster. When the signals indicate a discrepancy, the controller sets a target pressure difference and sends a target pressure difference signal, which is based on the target pressure difference, to the solenoid such that the control valve operates at the target pressure difference. The controller computes the torque for driving the compressor based on the target pressure difference signal and determines a target engine torque based on the compressor driving torque. The controller controls the engine based on the target engine torque.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.